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Knocking problems

98-XJ-Nate

NAXJA Forum User
Location
portland,OR
Hey I have a question for anybody that could help me?!

I have a 98 XJ with most the drivetrain stock...When I'm running at an idle the motor begins to make a strange knocking sound...it seems to be coming from the lower end of the motor and does not knock in time with the motors RPM's...?..As soon as I give it ANY throttle the knock goes away and the motor runs smooth as ever....Also when I shut it off the motor makes a last few clunking sounds. I'm planning on pulling the oil pan to see if i can notice anything but im not very mechanical !!

Has any one had a similar problem or offer any advise?!!
 
how does your oil pressure look? Sounds like a rod bearing. I was hearing/feeling a slight knock when I started my engine, and I thought it might be a rod bearing, I had to replace my rear main seal, so I went ahead and put all new rod bearings in. The same "knock" is still there.. so I assume it's normal. The original bearings actually didn't look too bad. Which is surpising considering it has 260,000 miles on it, and had such a bad oil leak, I'm sure it has been run low on oil several times. It would leak a quart of oil like every 30 miles. There is so much oil on the undercarriage I can tell it was driven with that leak a LONG time.
Anyways.. your oil pressure should be down a little bit if it's a rod bearing. You might try a thicker oil, 10w 40 if you aren't already using it,and if you are try 20w 50. And.. if you really want to fix it right..drop the pan and replace the bearings. They only cost about $30.
 
just a shot in the dark.... the plate on the front of the transmission may be loose. Mine was loose once and rattled like hell @ idle. I know you said it was a "knock" but who knows. just a thought
 
Hey thanx for the sugenstions so far guys...! My oil pressure seems to be fine and there are no leaks. I read some ware that it could be my flex plate and a few other "possibilities" that I'm going to look at in the morning...

Thanx again so far..
 
A friend of mine had the same problem in a 97 XJ 4.0. He noticed the "knock" around 110,000 miles. We swore up and down that it was a rod knock. He bought a remanned motor without looking into it further. When we pulled the original motor... The torque converter bolts had loosened up and egged the flexplate holes almost a half inch. He put the new motor in anyway and stashed the original...

1 year later my 2000 XJ had the notorious head cracking problem and I didn't realize it... The antifreeze wiped the bearings, crank, cam, lifters, and pretty much everything that sees friction. So I opened up my buddy's 97 motor and checked the bearings (rod and mains). They hardly had any wear at all. So I dropped it in my 2000. It runs flawless.

Definately check the 4 torque converter bolts.
 
I just recently developed the exact same problem. I only hear the noise at idle. I poked my head under there and it sounds like its coming from the bottom end of the motor and towards the rear of the block.

The only new changes I have noticed recently is the oil pan is leaking from the drivers side bolts that hold the oil pan in- it looks like oil is seeping from four of the bolts. Thee is some oil splatter back toward the rear main seal, but I am not sure if the rear main is leaking or if it is the oil pan gasket causing this. My oil loss is minimal. I don't have to add any oil between changes.
 
My guess would be the pan unless you've got ultra high mileage on the engine. We have 5 xj's in my crew that are from 95-00 models. We haven't had one rear main go bad. It was always the pan gasket. I would try tightening it up first. If that doesn't stop it go for the gasket and you can also do the seal while you go the pan off.
 
I'm begining to think its the torque converter bolts from reading and help from every one hear. I probobly wont have a chance to get under there untill this weekend due to work but I will post it if it is!! Thanx a ton !
 
I have this same problem. I can barely hear it. You know, it's there but everyone has to be quite and you hold your head just the right way.

It gets louder and then goes away, then comes back, in a cycle.

Where is this flex plate!?!?!
 
x2 :dunno:
 
just a shot in the dark.... the plate on the front of the transmission may be loose. Mine was loose once and rattled like hell @ idle. I know you said it was a "knock" but who knows. just a thought
Just fixed that on mine today. Oddly, it was fine until I replaced my exhaust manifold a few weeks ago, then it started knocking like mad.

Three out of four flexplate bolts were loose. Tighten them up and sure enough, it idles quietly(ish) again. I do need another inspection cover though as this one's broken.

Jim www.yuccaman.com
 
Where do you get access to check the flex plate bolts? I am going to check mine and see if this fixes my problems.
Pull the inspection cover off the front of the tranny. Grab a 15mm wrench and tighten the four bolts holding the flexplate to the torque converter. You can only get to one at a time so tighten it and use it to turn the flexplate to access the next one.

Jim www.yuccaman.com
 
Pull the inspection cover off the front of the tranny. Grab a 15mm wrench and tighten the four bolts holding the flexplate to the torque converter. You can only get to one at a time so tighten it and use it to turn the flexplate to access the next one.

Jim www.yuccaman.com

I'll have a look, but does the flex plate mount between the torque converter and the crank shaft?
 
just take the plate off your flywheel and tighten up the four bolts that connect the flywheel .....just get under there and tighten all the bolts you see !! lol
 
I tried this but couldn't get the damn thing to turn...even with everything in neutral...maybe i'm retarded, but do I need to jack it up or something?
 
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